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US-12628550-B2 - Solvent annealing

US12628550B2US 12628550 B2US12628550 B2US 12628550B2US-12628550-B2

Abstract

A post-deposition treatment universally applicable to a wide range of perovskite solar cell configurations and architectures. The methodology yields significant improvements in device efficiency and lifetime coupled with a reduction in inherent batch-to-batch variability in all performance metrics. Such improvements are achieved following an aerosol-induced recrystallisation of solution-deposited MAPbI 3 thin films that result in a significant enlargement and improved homogeneity of grain size. The aerosol treatment is demonstrated as being suitable for a range of active layer thicknesses, interlayer choices, architectures and device active areas.

Inventors

  • Joseph Briscoe
  • Sinclair Ryley Ratnasingham

Assignees

  • QUEEN MARY UNIVERSITY OF LONDON

Dates

Publication Date
20260512
Application Date
20210719
Priority Date
20200720

Claims (20)

  1. 1 . A method of solvent annealing comprising: exposing a perovskite layer to a laminar flow of a solvent aerosol, wherein the laminar flow produces a boundary layer between the laminar flow and the perovskite layer; and heating the perovskite layer to a predetermined temperature ranging from 50° C. to 200° C. during the exposing.
  2. 2 . A method according to claim 1 wherein the exposing is performed for a period greater than 2 minutes.
  3. 3 . A method according to claim 1 wherein the exposing is performed for a period less than 10 minutes.
  4. 4 . A method according to claim 1 wherein the solvent is a polar solvent.
  5. 5 . A method according to claim 4 wherein the solvent is selected from the group consisting of: N,N-Dimethylformamide Water Methanol Ethanol Isopropanol 2-Methoxyethanol Acetone Acetonitrile Ethyl acetate Chlorobenzene Dimethyl sulfoxide.
  6. 6 . A method according to claim 1 wherein the perovskite layer is formed of a perovskite material with the formula A 1 p A 2 q A 3 r B(X 1 s X 2 t X 3 u ) 3 , in which: A 1 , A 2 and A 3 are each independently caesium, rubidium, a C 1-5 alkylamine cation, a C 1-5 alkyldiamine cation such as formamidinium, an imidazolium cation, or guanidinium; p q and r are each independently 0 to 1, provided that p+q+r=1; B is Pb or Sn; X 1 , X 2 and X 3 are each independently a halide or a pseudohalide; and r, s t and u are each independently 0 to 1, provided that s+t+u=1.
  7. 7 . A method according to claim 6 wherein the perovskite layer is formed of a material selected from the group consisting of: CH 3 NH 3 PbI 3 Cs 0.15 (HC(NH 2 ) 2 ) 0.85 Pb(I 0.95 Br 0.05 ) 3 CH 3 NH 3 PbI 0.82 Br 0.12 Cs 0.15 (HC(NH 2 ) 2 ) 0.85 Pb(I 0.9 Br 0.1 ) 3 Cs 0.1 (HC(NH 2 ) 2 ) 0.9 Pb(I 0.95 Br 0.05 ) 3 HC(NH 2 ) 2 PbI 3 .
  8. 8 . A method according to claim 1 wherein the perovskite layer is formed of α-phase FAPbI 3 or α-phase FAPb(I 3-x Br x ) in which x is greater than zero and less than three.
  9. 9 . A method according to claim 8 wherein the predetermined temperature ranges between 90° C. to 110° C.
  10. 10 . A method according to claim 8 wherein the exposing is performed for a period of less than 10 minutes.
  11. 11 . A method according to claim 1 wherein the solvent is aerosolised in a carrier gas.
  12. 12 . A method according to claim 11 wherein the flow rate of the carrier gas is in the range of 0.1 l/min to 1.5 l/min during the exposing.
  13. 13 . A method according to claim 1 , further comprising doping the perovskite, wherein the aerosol further comprises one or more additional components for the doping of the perovskite.
  14. 14 . A method according to claim 1 wherein the aerosol further comprises one or more passivation additives.
  15. 15 . A method according to claim 1 wherein the aerosol further comprises components to form organic charge transport and/or contact layers, the components including one or more of: Phenyl-C61-butyric acid methyl ester, Bathocuproine, non-fullerene acceptors, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate or poly(triaryl amine).
  16. 16 . A method according to claim 1 wherein the aerosol further comprises one or more salts.
  17. 17 . A device incorporating a perovskite layer treated by a solvent annealing method according to claim 1 , wherein the device includes a photovoltaic cell, a light emitting diode, a photodetector or a detector of ionising radiation, wherein the method increases grain size while controlling surface roughness of the perovskite layer.
  18. 18 . A method according to claim 11 , wherein the carrier gas is N 2 .
  19. 19 . A method according to claim 16 , wherein the one or more halide salts are selected from the group consisting of MACl, MAI, FAI, FABr, CsI.
  20. 20 . The method according to claim 1 , wherein the boundary layer is a stable boundary layer.

Description

FIELD The present invention relates to methods of treatment of material layers, in particular solvent annealing of perovskite layers. BACKGROUND Organic-inorganic metal halide perovskite materials have had significant impact across a variety of emerging optoelectronic platforms, extending beyond their initial use in photovoltaics (PVs), to create disruption in the light emitting diode (LED), photodetector (PD) and thin film transistor (TFT) research fields. Within the PV field the progress of perovskite solar cell (PSC) development has been underpinned by simultaneous advances in thin-film deposition, compositional modification, changes to the charge selective interlayers, interface modification and the incorporation of a wide variety of additives. Many of these strategies depend on the precise control of interlayer thickness as well as additive and dopant concentration. Typically, these values are already incredibly low, thus inadvertently these strategies for improvement may place significant constraints on future high-volume manufacturing. Grain boundaries (GBs), whilst unavoidable in solution deposited PSCs, are unwanted microstructural features. They tend to host crystallographic defects e.g. vacancies, interstitials, anti-sites, all of which create intra-bandgap states that act as electronic traps. GBs are also reported to have several other drawbacks: i) fast channels for ionic transport thus contribute significantly to device hysteresis, ii) pathways for oxygen ingress and iii) susceptible areas for the formation of impurity phases [Ref. 10]. In particular, GBs parallel to the substrate present additional barriers to charge extraction in PSC, due to the out of plane charge transport. To circumvent these issues, efforts have been made to passivate GBs through additive engineering, directing crystal growth, promoting larger grains and fabricating PSCs from single crystals. One means of reducing the number of GBs has been through solvent vapour annealing (SVA), a concept taken from the organic semiconductor community [Ref 1, Ref 2]. SVA has been an effective post-deposition treatment for PSCs, improving film crystallinity whilst not relying on complex compositional modifications to precursor solutions or as-deposited films [Refs 3 to 7]. SVA involves the introduction of solvent vapour during the crystallisation process of thin films, which lowers the diffusive energy barrier and allows for the coalescence of grains. In practice, the process is typically achieved by overturning a petri dish, or similar vessel, over a solvent rich thin film or a small reservoir of solvent. This traps the solvent vapour near the vicinity of the film. Typically, solvent exposure time and temperature are the critical variables, as there is a balance between grain growth and diminishing surface homogeneity [Ref 8]. Different solvents can also have different effects [Ref. 9]. SUMMARY A technique to improve performance of devices including perovskite material layers is desirable. According to the invention there is provided a method of solvent annealing comprising exposing a perovskite layer to a laminar flow of a solvent aerosol. The method may further comprise heating the perovskite layer to a predetermined temperature (desirably in the range of from 50° C. to 200° C). during the exposing. The exposing may be performed for a period greater than 2 minutes, preferably greater than 4 minutes. The exposing may be performed for a period less than 10 minutes, preferably less than 7 minutes. Desirably the solvent is a polar solvent. More desirably the solvent is selected from the group consisting of: N,N-DimethylformamideWaterMethanolEthanolIsopropanol2-MethoxyethanolAcetoneAcetonitrileEthyl acetateChlorobenzeneDimethyl sulfoxide Desirably the perovskite layer is formed of a perovskite material with the formula A1pA2qA3rB(X1sX2tX3u)3, in which: A1, A2 and A3 are each independently caesium, rubidium, a C1-5alkylamine cation, a C1-5alkyldiamine cation or a guanidinium cation;p q and r are each independently 0 to 1, with the proviso that p+q+r=1;B is Pb or Sn;X1, X2 and X3 are each independently a halide or a pseudohalide; ands t and u are each independently 0 to 1, with the proviso that s+t+u=1. More desirably the perovskite layer is formed of a material selected from the group consisting of: CH3NH3PbI3 Cs0.15(HC(NH2)2)0.85Pb(I0.95Br0.05)3 CH3NH3PbI0.82Br0.12 Cs0.15(HC(NH2)2)0.85Pb(I0.9Br0.1)3 Cs0.1(HC(NH2)2)0.9 Pb(I0.95Br0.05)3 or is selected from the group consisting of CH3NH3PbI3 Cs0.15(HC(NH2)2)0.85Pb(I0.95Br0.05)3 CH3NH3PbI0.82Br0.12 Cs0.15(HC(NH2)2)0.85Pb(I0.9Br0.1)3 Cs0.1(HC(NH2)2)0.9 Pb(I0.95Br0.05)3 HC(NH2)2PbI3 FAPbI3 (e.g. α-phase FAPbI3)FAPb(I3-xBrx) (e.g. α-phase FAPb(I3-xBrx)) in which x is greater than zero and less than three Desirably wherein the solvent is aerosolised in a carrier gas, e.g. N2. Desirably the flow rate of the carrier gas is in the range of 0.1 l/min to 1.5 l/min during the exposing. Desirably the a